Poor fertility in cattle is estimated to cost $1 billion annually in the US. It is useful for farmers to synchronize the estrus of animals such as cattle (both dairy and beef) sheep, goats, horses, or the like where artificial insemination is practiced. By way of example, dairy cows must be impregnated once a year to maintain a lactation cycle in which milk is produced for ten months at a time with two month rest periods in between during which the cow is dry. Given the gestation period of a dairy cow, the objective is to impregnate the cow within 83 days after calving. The efficient management of a dairy herd thus requires that the cows be maintained at the peak of fertility to ensure re-impregnation within 83 days.
Accordingly, cattle producers and dairy scientists are continuously searching for nutritional supplements that promote dairy cow fertility. Fish oil fatty acids have become the focus of numerous research programs that seek to capitalize on their nutritional and physiological properties. WO 99/66877 to Amir et al. discloses the use of omega-3 fatty acids of fish oil origin to increase fertility in animals including cattle. Among the omega-3 fatty acids disclosed are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). WO 02/054886 to Lanna et al. provides for improved reproductive function in cows which were fed one daily dose of 150 g/day of calcium salts containing 70% fatty acids. Conjugated linoleic acid (CLA) isomers make up 60% of the fatty acids contained within the calcium salt formulation. Of the total CLA isomers approximately 24% was c/t 9, 11; 35% was c/t 10, 12; 15% was c/t 8, 10; 17% was t11, t13 and the remaining 9% was others. Knowing the concentrations of the individual isomers, a calculation of the amounts of cis-9, trans-11 and trans-10, cis-12 indicates that the dose used in this reference was about 15 g of cis-9, trans-11 and 22 g trans-10, cis-12 per day. Because the composition used in this reference contained significant amounts of several isomers, the effects could not be attributed to specific isomers. Additionally, because only a single concentration was used, there was no determination of a useful dosage for improvement of reproductive function. Further, the inventors describe how an improvement in energy balance allowed for the better reproduction. It is well known for all mammals that reproductive performance is compromised if nutrient intake is inadequate and this can be overcome by improving energy balance (Wade et al., 1996, Am. J. Physiol. 270:E1-E19).
Bernal-Santos et al. (2003, J. Dairy Sci. 86:3218-3228) disclose the administration of a single dose of 30 g/day of a CLA mixture comprising a mixture of various isomers. Of the total CLA isomers approximately 25.1% was c9, t11; 28.9% was t10, c12; 9.2% was t8, c10; 16.1% was c11, t13 and the remaining 20.7% was others. The authors concluded that no adverse effects were observed on conception and maintenance of pregnancy. However, the authors acknowledge that due to the limited number of animals in their study, they were unable to make any definitive conclusions regarding reproductive variables.